Water turbidity dynamics using random forest in the Yangtze River Delta Region, China

Xingna Lin; Ming Wu; Xuexin Shao; Guozhi Li; Yifeng Hong

doi:10.1016/j.scitotenv.2023.166511

Water turbidity dynamics using random forest in the Yangtze River Delta Region, China

Sci Total Environ. 2023 Dec 10:903:166511. doi: 10.1016/j.scitotenv.2023.166511. Epub 2023 Aug 25.

Authors

Xingna Lin¹, Ming Wu², Xuexin Shao³, Guozhi Li⁴, Yifeng Hong⁵

Affiliations

¹ Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou 311400, China. Electronic address: linxingna@caf.ac.cn.
² Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou 311400, China. Electronic address: hangzhoubay@126.com.
³ Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou 311400, China.
⁴ East China Academy of Inventory and Planning, National Forestry and Grassland Administration, Hangzhou 311400, China.
⁵ East China Academy of Inventory and Planning, National Forestry and Grassland Administration, Hangzhou 311400, China. Electronic address: hongyifeng007@126.com.

PMID: 37633384
DOI: 10.1016/j.scitotenv.2023.166511

Abstract

Turbidity is a water quality indicator that is essential for the sustainable development of aquatic ecosystems and the protection of biodiversity. The turbidity of different water surfaces and its response mechanisms to regional climatic factors and human activities in the Yangtze River Delta Region (YRDR), an important rapid economic development region in China, remain poorly understood. To enhance the knowledge of turbidity variations and dominant drivers of YRDR water surfaces, a complete long-term turbidity series was obtained using Landsat images from 1990 to 2020. The results show that the turbidity trend differed from -1.3 NTU/yr to 0.7 NTU/yr in different water surfaces. Turbidity decreased significantly in the mainstream of the Yangtze River (MYR), aquaculture ponds (AP) and other water bodies, whilst increasing significantly in the medium lakes (ML) and mainstream of the Qiantang River (MQR). Meanwhile, no significant changes in turbidity were observed in the great lakes (GL) and small lakes (SL). Rather than climatic factors, urbanisation and decreasing wastewater discharge were the dominant drivers of turbidity trends during the study period. In addition, ecological engineering in AP increased water transparency. The Three Gorges Dam also decreased turbidity in MYR. Increasing turbidity in the downstream of MQR was driven by increasing seasonal water surfaces and reclamation projects near Hangzhou Bay. GL faced no significant increase in turbidity due to the offset of afforestation to urbanisation-induced turbidity increase. These findings provide important information for government decision-making for subsequent aquatic environmental protection and restoration in the YRDR.

Keywords: Dominant drivers; Random forest; Turbidity; Urbanisation; Wastewater discharge.